PC-driven prototyping adds design confidence

The use of a PC-based CNC machine has helped a manufacturer improve the quality of its designs by allowing the company to make more prototypes.

A company's industrial designers were very concerned with how a product feels in the hand.

Although they use solid modelling to document their designs, viewing solid models on-screen doesn't give the sense of how it feels to hold the object.

Only prototypes can do that.

The industrial design company in question specialises in ergonomically designed handheld products such as hand tools, game controllers and consumer electronics.

The design process begins with sketches as designers put their ideas down on paper which they present the sketches to clients and often include foam models so the client has something to hold.

Foam models are made by transferring the sketches to a CAD program then the 2D shapes from Vellum are used to make templates and these are used to guide the cutting of Dow Blue Foam with a hot wire.

It takes a skilled model maker about one day to make a blue foam model and while these models are good for initial concepts, they are not highly accurate since the process of cutting them requires some interpolation between surfaces.

Once a customer has looked at the sketches and foam models and narrowed down the possibilities to two or three concepts the designers need solid modelling at this stage a feel for the product and to show the customer.

At this point more accuracy is required than can be obtained with blue foam.

These prototypes made by an outside agency were accurate, high quality, and could be turned around quickly for an additional fee.

However the main drawback to having an outside vendor do this work was that the cost limited the number of prototypes that could be made at this point in the design.

A designer who wanted to feel whether a certain shape was comfortable to hold, for example, might choose not to get a prototype because of the cost.

As they were creating a solid model of the design it made sense to use model geometry to produce prototypes in-house.

At first, the company considered 3D printers as a means of doing this as these relatively new devices are less expensive versions of larger rapid prototyping systems and are designed to create quick prototypes for design reviews.

However, the prototypes produced with these systems require a great deal of finishing taking at least a day of sanding for most products.

This proved much to time consuming and they did not want to allot that kind of time to model production and in addition the high of a 3D printer and the fact it was not highly accurate made this a poor option.

The answer came for producing prototypes from solid models was to machine them and a PC-driven CNC router from Isel proved to be the solution.

The machine was designed for production routing and drilling on a wide variety of materials including wood, plastic, MDF, solid surfacing materials and nonferrous metals.

The technical specifications of the machine purchased included a working area for the router of 500 x 500mm and z-axis height of 200mm.

The table features a rapid travel rate of 900mm per minute, a z-axis cutting force of 100kg maximum, 0.013mm resolution and repeatability.

A key feature of the servo system is its ability to cut 3D continuous contours at up to 5000mm per minute, far faster than most machining centres.

Now, when a designer wants to make a quick prototype from Pro/Engineer data, toolpaths are first generated in Pro/Manufacture and then sent to the model shop to be produced.

It takes about a day to programme the machine and produce a prototype, so by the next day a designer has a part to examine surfaces, fit together, or see what feels good in his hand.

Thanks to the accuracy of the machine finishing time is minimal.

The machine has a positioning accuracy of +1mm in 300 mm, a repeatability of 0.01mm and antibacklash ball screws for play-free motion.

These screws have excellent power transmission due to the rolling ball contract between the nut and screws, this type of contact ensures low friction, low wear, and long life.

The ball screws also make it possible to produce parts to the machine resolution of 0.013mm and for the model makers this means that a part can be sanded down with sandpaper in about 20 to 30 minutes.

The machine runs on average 20 hours per week, although there are situations when it runs constantly.

The CNC machine is very stable and reliable being constructed from extruded aluminium profiles that can support all the soft materials used.

The machine has four hardened and ground steel shafts and eight recirculating bearings in each axis.

This shaft-and-bearing system produces very smooth, play-free motion and an extremely rigid system that produces high-quality cuts.

The problems of noise and dust that are unacceptable in an office environment were solved by enclosing the router in a cabinet constructed from the same aluminium extrusions.

Before acquiring the CNC machine the prototypes made by an outside service cost time and money, limiting the number of prototypes used in the course of a design.

After installing the CNC machine, the cost of a typical prototype dropped by 60%, allowing designers to make more samples to better refine a design.

The prototypes produced on the Isel machine have been invaluable in that they give designers and clients an accurate part to hold in their hands improving the quality of its designs.

Another important benefit of having the machine is that it impresses clients and prospective clients having the ability to mill parts in-house and showing them how quickly they can get to hard prototypes, has helped close several sales.

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